Biological activities of rishitin, an antifungal compound isolated from diseased potato tubers, and its derivatives

Rishitin, a norsesquiterpene alcohol, found in infected, resistantpotato-tuber tissue completely inhibited zoospore germinationand germtube elongation of Phytophthora infestans (MONT.) DEBARY at 10^–3M. There was little difference in sensitivityto rishitin among races of Phytophthora infestans. IAA-inducedelongation of Avcna coleoptile sections and GA₃-induced elongationof wheat leaf sections were also inhibited by rishitin. Theinhibition of IAA-induced elongation of Avena coleoptiles wasrelieved to some extent by increasing IAA concentration. However,little relief of the inhibition of GA₃-induced elongation ofwheat leaf sections was obtained by increasing GA₃ concentration.No plant injury was observed at this concentration of rishitin(10^–3M). Examination of a series of rishitin derivatives indicated thatthe hydroxyl group at C-3 is indispensable for antifungal activity.This activity was intensified by saturating the double bondbetween the rings of rishitin and/or that of the isopropenylgroup at C-7, though activity decreased when oxygenated functionalgroups were introduced into the side chain. Aromatization of the A ring did not lower biological activities.The antifungal activities of most rishitin derivatives almostparalleled their activities as plant growth retardants. However,some compounds without antifungal activity were active as growthretardants. ¹Studies on the phytoalexins (5). (Received August 14, 1968; )     

DISPERSAL PATTERNS OF THE GIANT AFRICAN SNAIL, ACHATINA FULICA (FERUSSAC) (STYLOMMATOPHORA: ACHATINIDAE), EQUIPPED WITH A RADIO-TRANSMITTER

The dispersal pattern of the African giant snail, Achatina fulica(Férussac) was examined by radio-tracking for six months.They showed typically nocturnal locomotory activities. Theiractivities differed among three developmental stages; juvenile,young adult, and old adult. Juveniles dispersed for the longestdistances. The most active juvenile moved 500 m in 6 months.Young adults and old adults travelled only within a narrow area,although the dispersal range for young adults was greater thanthat of old adults. (Received 15 September 1992; accepted 11 December 1992)     

PHENOL METABOLISM IN RELATION TO DISEASE RESISTANCE OF POTATO TUBER: I. ACTIVITIES OF PHENOL OXIDASE AND SOME ENZYMES RELATED TO GLYCOLYSIS AS AFFECTED BY CHLOROGENIC ACID TREATMENT

Disks of potato tubers, 0.5 mm in thickness, were treated witha mixture of chlorogenic and ascorbic acids. When they werenot washed with water after the treatment, they became brown.Activities of phenol oxidase and glutathione reductase and o-diphenolcontent increased more rapidly in these disks than in untreatedcontrol. Activity of the pentose phosphate pathway was increasedby the treatment, while that of EMDEN-MEYERHOF-PARNAS pathwaywas greatly inhibited. In washed unbrowned disks, the changesin those activities were negligible or smaller than those inthe browned disks, although chlorogenic acid which had permeatedremained in the tissue after washing. Oxidized products of chlorogenicacid and possibly of ascorbic acid may be a trigger in thisalteration in metabolism. Malonate and streptomycin also induced similar effects on thephenol metabolism in the tuber disks. Increases in o-diphenolcontents and in phenol oxidase activity were caused probablyby preferential inhibition of EMDEN-MEYERHOF-PARNAS pathwayand tricarboxylic acid cycle. These results are discussed inrelation to the mechanism of disease resistance of potato tuber. (Received May 6, 1966; )